1917] BROOKS—PERMEABILITY 231 
then tested, gave no reaction. This method, although positive, 
can yield only qualitative data. 
As a method for the investigation of protoplasmic permeability, 
quantitative analysis of tissue extracts involves several important 
sources of error, among which may be mentioned the presence of 
salts in the intercellular spaces and in the cell walls, where they 
may be held in solution or by adsorption, variations of the con- 
centration and constitution of expressed juices dependent on the 
pressure used in extraction (cf. MamELI 30), and, most serious of 
all, adsorption or chemical union of the salts within ‘the cell. Thus, 
while aluminium ions might displace potassium ions in an adsorp- 
tion compound, sodium ions might displace the Sapien ions to a 
small extent only. In this way the free aluminium content of the 
cell would remain low, and the original rate a endosmosis of 
aluminium salts would be maintained, while that of sodium salts 
would steadily deorease as the free sodium-content of the cell 
increased. A similar effect might be produced by the formation of 
hydrates of aluminium and sodium; the former being insoluble 
would form a precipitate, while the latter would sain in solution." - 
The relative permeability of the t would then 
be made to appear other than it actualy wie The last error also | 
affects methods involving the amount of salt taken by tissues from 
by experiments of this type, such | 
- PP. 453 ff.), PANTANELLI (51), DE Rurz: DE ‘LavIson el 56), Count 
and DE Rurz DE Lavison (4, 5), M (EURER (36), and many others. : 
PAINE (50), usi , drew the conclusion that yeast 
\a™s : = Doce aie 7 . ie 
cells are wholly i able to i Jif i ~ Its.2 eeeg! a x ae 
absorption of oe salts nates the yeast cells, b 
n pagilaieag cmaeyners 
